Wireless cellular networks are known. The area covered by the network is divided up into cells. Each cell is created by a base transceiver station BTS which is arranged to communicate with mobile devices such as, for example, mobile telephones, located in the cells
A number of different standards are known which govern the communication between mobile stations and base stations as well as with other network elements. One example of a currently known standard is the GSM standard (global system for mobile communication). This is a so-called second generation standard. At the present time, work is being carried out on the so-called third generation standard. In general, these third generation standards use code division multiple access CDMA in the radio interface between mobile stations and base transceiver stations. One of the current proposals for a third generation standard suggest using wide band CDMA (WCDMA) in the communication. With CDMA, a stream of bits or data has a spreading code applied thereto. The spreading codes distinguish the data intended for different mobile stations in the same cell and accordingly, the same frequency can be used at the same time to transmit the data to the mobile stations. Likewise, a number of mobile stations can transmit to the base station at the same time, in the same frequency band with the data being distinguished by different spreading codes. A single WCDMA BTS may support (create) one or several cells. A WCDMA cell is can be defined as a frequency and a given geographic area where the P-CCPCH (Primary-Common Control Physical Channel) can be received by a mobile station or the like.
There exist baseband and radio frequency RF processing units in a base transceiver station. Baseband processing units receive (bit) messages from a core network and prepare them for transmission via an air interface for example by performing channel encoding and spreading functionality. In some cases, modulation and upconversion, typically to an intermediate frequency, may be done at the baseband part of the base transceiver station. RF processing units convert the baseband signal up to the final radio frequency (which is around 2 GHz). Additionally, processing units that transfer data between the baseband and RF processing units may be needed. The data is passed between nodes in the base station in packet form.
The packet has a header part and a payload part. The header part will typically contain information such as address information, time stamp information and information identifying the type of data contained in the payload. The payload simply contains the message or data intended for the mobile station or base station.
The base station also provides a routing function and directs packets to the appropriate modulator for modulation, upconversion and transmission It should be appreciated that a base station will transmit on a number of different frequencies at the same time. Accordingly, different modulators may be provided for the different frequencies.
The base station can be regarded as being made up of a number of bus nodes. A received base band packet will pass through several of the nodes in order to be up converted to the radio frequency. The nodes may be provided by ASICs (application specific integrated circuits) or the like. It should be appreciated that one ASIC may provide more than one node.
It has been appreciated by the inventors that providing routing between the nodes and sufficient capacity on that routing for the various different packets requires a large resource. This is undesirable in that this increases the complexity of the base station as well as its size. In other words, a large amount of band width is required for data transfer from baseband to RF, and vice versa.
Another potential problem with base stations relates to latency. In particular, for CDMA or wide band CDMA, it is important to minimise the latency of the data packets passing through the base transceiver station.